1. Field of the Invention
The present invention generally relates to a motor control method and, more particularly, to a motor control method capable of controlling the rotational speed and rotational direction of a motor by a single signal.
2. Description of the Related Art
Conventionally, a fan wheel of a fan in an electric device is usually designed to be rotated in a predetermined direction by a motor of the fan for efficiently dissipating the heat generated during operation of the electric device. However, dust coming along with the airflow drawn into the electric device can be easily accumulated inside the electric device. Therefore, the motor usually drives the fan wheel to rotate in a reverse direction opposite to the predetermined direction for a while, such as 5 seconds, after the electric device is just started so as to execute a dust-removing process for the electric device, and then drives the fan wheel to rotate in the predetermined direction for cooling the electric device after the dust-removing process is finished.
Referring to FIG. 1, a block diagram of a motor control system implementing a conventional motor control method is shown, wherein a first signal generator 91 and a second signal generator 92 electrically connect with a control unit 93, a driving unit 94 electrically connects with the control unit 93 and a motor 95, and the motor 95 connects to and rotates a fan wheel. In the motor control method, the first signal generator 91 generates a direction signal, which is preferably a logical signal such as a HIGH signal or a LOW signal, to include a direction command for operating a rotor of the motor 95 to rotate in a predetermined direction or a reverse direction opposite to the predetermined direction, and the second signal generator 92 generates a speed signal such as a PWM signal or a DC signal to include a speed command by the duty ratio of the PWM signal or the voltage level of the DC signal for controlling the speed of the rotor. The control unit 93 may produce a control signal according to the direction and speed commands, and the driving unit 94 will convert the control signal into a driving signal to drive the motor 95, so that the motor 95 can drive a fan wheel for heat dissipating or dust removing.
However, there are still some drawbacks of the conventional motor control method waiting to be overcome.
(A). The first and second signal generators 91, 92 have to respectively generate the direction and speed commands for driving the motor 95 in a desired direction with a desired speed. However, in some motor control systems that only generates a PWM signal, a circuit of this motor control system has to be modified for the additional direction control function since the PWM signal only includes the speed command. In other words, the conventional motor control method cannot be implemented by these motor control systems unless a circuit modification is done, and this will limit the use of the conventional motor control method apparently.
(B). It is known that the strength of a signal decays corresponding to a transmitted distance of the signal, and thus the transmission of the direction signal and the speed signal may result in a power consumption higher than that of a single signal including both the direction and speed commands.
(C). The motor 95 can normally operate only if both of the direction signal and the speed signal are safely received by the control unit 93. In other words, once any one of these two signals is missed or distorted, the control unit 93 will not be able to accurately generate the control signal for the driving unit 94 to drive the motor 95. Therefore, a possibility of incorrect operation of this conventional motor control method is higher than that of a motor control method using only a signal including both the direction and speed commands.
(D). Space and cost for the signal generator 91, 92 are larger than those for a single signal generator, while circuit complexity of the motor control system with the signal generator 91, 92 is higher than that of a motor control system only having one signal generator.
In light of this, it is desired to provide a motor control method that is capable of being implemented without circuit modification, lowers power consumption and fault possibility, and decreases required space, cost and circuit complexity of a motor control system implementing the motor control method, so as to save power and increase operation reliability.